Compounds corresponding to the formula: AlArfQ1Q2, or a dimer, adduct, or mixture thereof and further mixtures with aluminum compounds of the formula: AlArf3, where: Arf is a fluorinated aromatic hydrocarbonyl moiety of from 6 to 30 carbon atoms; Q?1 is Arf¿ or a C¿1-20? hydrocarbyl group, optionally substituted with one or more cyclohydrocarbyl, hydrocarbyloxy, hydrocarbylsiloxy, hydrocarbylsilylamino, hydrocarbylsilyl, silylhydrocarbyl, di(hydrocarbylsilyl)amino, hydrocarbylamino, di(hydrocarbyl)amino, di(hydrocarbyl)phosphino, or hydrocarbylsulfido groups having from 1 to 20 atoms other than hydrogen, or further optionally, such substituents may be covalently linked with each other to form one or more fused rings or ring systems; and Q?2¿ is an aryloxy, arylsulfide or di(hydrocarbyl)amido group, optionally substituted with one or more hydrocarbyl, cyclohydrocarbyl, hydrocarbyloxy, hydrocarbylsiloxy, hydrocarbylsilylamino, hydrocarbylsilyl, silylhydrocarbyl, di(hydrocarbylsilyl)amino, hydrocarbylamino, di(hydrocarbyl)amino, di(hydrocarbyl)phosphino, or hydrocarbylsulfido groups having from 1 to 20 atoms other than hydrogen, or, further optionally such substituents may be covalently linked with each other to form one or more fused rings or ring systems, said Q2 having from 3 to 20 atoms other than hydrogen are useful as activators for olefin polymerizations.